NH3 LiNO3 Research Articles

Effect of salt on the performance of ammonia absorption refrigeration cycle: A simulation study

To overcome the drawbacks associated with conventional binary mixtures (NH3-H2O and H2O-LiBr) in the vapor absorption refrigeration system (VARS), salt is added to the NH3-H2O mixture. The present simulation study analyzes the influence of adding LiBr and LiNO3 salts within a salt mass fraction range of 0 to 35% on the coefficient of performance (COP) of the NH3-H2O cycle. The simulations are conducted using Aspen Plus software. Furthermore, the influence of generator temperature on the COP and evaporator capacity of the ternary NH3-H2O-LiBr and NH3-H2O-LiNO3 cycles are also studied. The simulation results demonstrate that adding LiBr and LiNO3 salts improves the COP and reduces the initial temperature requirement in the generator of the VARS. Specifically, the NH3-H2O-LiBr cycle achieves the highest COP of 0.645 at an NH3 mass fraction of 55% and a LiBr mass fraction of 25%. This represents an 8.81% improvement compared to the COP of the NH3-H2O cycle. Similarly, the NH3-H2O-LiNO3 cycle exhibits the peak COP of 0.603 with the same NH3 mass fraction and LiNO3 mass fraction of 20%, which is 2.2% greater than the COP of the NH3-H2O cycle. Under similar operating conditions, the COP of the NH3-H2O-LiBr cycle is greater than that of the NH3-H2O-LiNO3 cycle.

Self-adapting double and triple-lift absorption cycles for low-grade heat driven cooling

• Five multiple-lift self-adapting NH 3 H 2 O and NH 3 –LiNO 3 cycles are presented. • The self-adapting concept automatically assures optimum cycle operation. • COP ranges are 0.20–0.35 for double-lift cycles and 0.1–0.25 for triple-lift cycles. • Higher efficiency and wider working range are achieved using more than one pump. • NH 3 H 2 O pair is more efficient at low lift, NH 3 –LiNO 3 at high lift. Multiple-lift absorption cycles are an interesting option for cooling and refrigeration driven by waste or renewable heat. Compared with single effect cycles, they allow higher thermal lift or lower thrust, but they often require the use of controlled valves, which can cause stability and control issues. The self-adapting concept, firstly introduced in the two-pump series-flow double-lift cycle, replaces the valve with a phase separator, overcoming this drawback. In this work, five new cycle layouts, incorporating the self-adapting concept, are presented: the one-pump series-flow double-lift cycle and four triple-lift cycles. The cycles are compared in terms of COP and heat duties under various conditions, using NH 3 H 2 O and NH 3 –LiNO 3 as working pairs. It is found that the double-lift cycles have a COP in the range 0.35–0.20, about 0.1 higher than the triple-lift cycles. However, triple-lift cycles accept cooling water temperature up to 8 °C higher. Cycles with multiple pumps have higher efficiency than single-pump cycles, especially at high lift conditions. The use of NH 3 H 2 O as working pair guarantees higher COP at low thermal lift, while NH 3 –LiNO 3 has wider operating range and better performances at high thermal lift.

Boiling Heat Transfer Coefficients in a Falling Film Helical Coil Heat Exchanger for the NH3–LiNO3 Mixture

This paper reports the experimental data of boiling heat transfer coefficients for the ammonia–lithium nitrate mixture in a laminar falling film. The analyzed heat exchanger consists of a shell with an internal helical coil. More than one hundred test runs were carried out in steady-state conditions to determine the boiling heat transfer coefficients at generation temperatures, concentrations, and mass flow rates typical of absorption cooling systems of capacities between 5 and 10 kW. Ammonia vapor was produced at generation temperatures between 80 °C and 105 °C obtaining boiling heat transfer coefficients between 85 and 340 W/m2K. Semi-empirical correlations were used by diverse authors to correlate the experimental data. A new correlation was proposed with which the best adjustments were obtained. Also, the influence of the heat flux, the refrigerant solution mass flow rates, and the exit vapor qualities were analyzed in the boiling heat transfer coefficients.

Performance comparison and optimal parameters evaluation of solar-assisted NH3–NaSCN and NH3–LiNO3 type absorption cooling system

This paper represents the detailed thermodynamic study to compare the performance of solar energy-assisted ammonia–sodium thiocyanate (NH3–NaSCN) and ammonia–lithium nitrate (NH3–LiNO3) absorption cooling system coupled with various solar collectors. A 15-kW absorption cooling system at evaporator temperature − 5 °C is considered and analyzed integrated with flat plate collectors (FPC), evacuated tube collectors (ETC), flat plate with compound parabolic collector reflectors and parabolic trough collectors (PTC) connected with storage tank to operate the absorption system. In this study, minimum generator (cut-off) temperature to operate the system is evaluated for both NH3–NaSCN and NH3–LiNO3 working pairs. Analysis of variance is performed to find out most critical operational parameters for cut-off temperature. In addition, the influence of heat source temperature on energetic, exergetic and economic aspects of systems is depicted. Exergetic optimization of each system estimated the required optimum collecting area for cooling. Required capital cost of solar collector at optimized area is also evaluated. The performance comparison from thermodynamic perspectives shows that NH3–LiNO3 coupled with ETC is superior to NH3–LiNO3 coupled with FPC. NH3–LiNO3 VARS coupled with PTC exhibited 23% higher value of optimized cost and 0.7% higher value of $$\eta_{{{\text{II}},{\text{system}}}}$$ in comparison with NH3–LiNO3 integrated with ETC. Key performance indicator is evaluated for the selection of optimum system. On the basis of key performance indicator, NH3–LiNO3 system coupled with ETC is recommended by considering thermodynamic and economic criteria.

Experimental evaluation on thermal performance of an air-cooled absorption refrigeration cycle with NH3–LiNO3 and NH3–NaSCN refrigerant solutions

This paper experimentally analyzes thermal performance of an air-cooled type single effect absorption refrigeration cycle with ammonia–lithium nitrate and ammonia–sodium thiocyanate solutions as working pairs. Ammonia/salt system has simple construction, low evaporating temperature (<0°C) and high working efficiency. Ammonia is one kind of environment-friendly refrigerants. Hence, ammonia/salt absorption refrigeration cycles are considered to be the most possible ones for practical application in small capacity refrigeration units. An experimental apparatus has been designed and built in Wuhan, China, to evaluate the cycle thermal performance of air-cooled type single effect ammonia/salts absorption refrigeration system. The experimental apparatus operates steadily under different working conditions. A set of tests have been conducted and the corresponding experimental data are measured and recorded to show the variation of the system performances with different system working parameters. For the NH3–LiNO3 system, the measured lowest evaporation temperature reaches −13.1°C with corresponding average system COP of 0.15, and the average refrigerating capacity is about 670W. For the NH3–NaSCN system, with a measured evaporation temperature of −7.5°C, the corresponding average COP is 0.20, and the average refrigerating capacity was about 590W. According to the experimental results, the actual measured COP of NH3–NaSCN system are in the range of 0.20–0.35, which are a little higher than that of NH3–LiNO3 system (actual measured COP ranging from 0.15 to 0.29). Under similar working condition, NH3–LiNO3 system can reach a lower evaporation temperature than that of NH3–NaSCN system. The experimental results of the present study demonstrate the feasibility and capability of ammonia/salt absorption refrigeration cycle for freezing purpose under air cooling conditions. Although the coefficient of performance of the experimental apparatus is below expectation while comparing with the theoretical results, optimization methods are put forward by the present paper for further research.

Influence of a compound parabolic concentrator in the performance of a solar diffusion absorption cooling system

This article presents the performance of a diffusion absorption cooling system that uses a solar compound parabolic concentrator (CPC) as the heat source. The cooling system uses lithium nitrate (LiNO3) and sodium thiocyanate (NaSCN) absorbent substances, and ammonia (NH3) as a refrigerant. The heat transfer fluids between the CPC and the cooling system studied were glycerol–water (C3H8O3–H2O), ethylene glycol–water (C2H6O2–H2O) and propylene glycol–water (C3H8O2–H2O). For the study of the solar cooling system, a mathematical model was developed and a simulator validated with experimental results of a properly designed CPC. The effects of the heat transfer fluid concentration and mass flow rate were evaluated against the coefficient of performance (COP). In addition, the work includes assessing the influence of the solar radiation and the ambient temperature on the solar cooling system COP. According to the results, the best options were the NH3–LiNO3 working mixture and the C3H8O3–H2O heat transfer fluid.

Exergy analysis of a novel air-cooled non-adiabatic absorption refrigeration cycle with NH3–NaSCN and NH3–LiNO3 refrigerant solutions

This paper presents a methodology of exergy analysis for ammonia-lithium nitrate and ammonia-sodium thiocyanate absorption refrigeration cycle which applies a novel air-cooled type non-adiabatic absorber to improve both the coefficient of performance and exegetic efficiency of the system under air cooling condition. A modified entropy calculation method for NH3/NaSCN and NH3/LiNO3 solutions is presented in this literature and different results are obtained comparing to previous research. In addition to the variation of solution temperature and pressure from specific working state to the reference state, the variation of solution concentration, which was always neglected by previous researchers in ammonia/salt solution exergy calculation, has been taken into account while analyzing the least potential of ammonia/salt solution for doing useful work, and a corresponding approach for specific exergy calculation is presented. The effects of generator temperature, absorber outlet temperature, absorber efficiency and other system parameters on system exergetic efficiency have been discussed in this study. Analysis results indicate that relatively high system performance can be obtained by air-cooled type ammonia/salt absorption refrigeration cycles when non-adiabatic absorbers are applied in these systems.

Optimum generator temperature to couple different diffusion absorption solar cooling systems

This paper presents the generator temperatures to achieve the highest efficiency in different solar diffusion absorption cooling systems. Ammonia-lithium nitrate (NH3–LiNO3) and sodium ammonia-thiocyanate (NH3–NaSCN) were examined as the working mixtures, and the flat-plate collector (FPC), the flat-plate collector improved (FPCI), the evacuated-tube collector (ETC) and the compound parabolic concentrator (CPC) were the thermal energy sources. The study was conducted with a simulation in steady-state conditions. The effects of the generator temperature on the global efficiency of each solar cooling system were studied. The results show that the FPC and the FPCI cannot activate the cooling system at evaporator temperatures below 0 °C and the ambient temperature is at 40 °C. At evaporator temperatures above 5 °C with an ambient temperature of 30 °C, all solar collector technologies activated different working mixtures. The optimum coupling temperatures were between 70 and 150 °C. The ETC/NH3–LiNO3 was between 5 and 54% relatively better than other technologies.

Comparison of the performance of single-effect, half-effect, double-effect in series and inverse and triple-effect absorption cooling systems operating with the NH3–LiNO3 mixture

This paper presents the performance comparison of five different configurations of absorption cooling systems operating with ammonia–lithium nitrate. The configurations are: i) single-effect, ii) half-effect, iii) double-effect in series, iv) double-effect inverse and v) triple-effect. Mathematical models were developed for each one of the systems. Coefficients of performance are reported for the systems as function of their main operating temperatures, such as: generation, absorption, condensation, and evaporation. The results showed that the lowest evaporator temperatures can be achieved with half-effect systems at the lowest generator temperatures with coefficients of performance around 0.3. The single-effect system is the simplest configuration since it requires fewer components in comparison to the other systems. Its coefficients of performance are almost twice higher than those obtained with half-effect systems but requiring higher generator temperatures. With double-effect systems it is possible to obtain coefficients of performance as high as 1.12 at condenser temperatures of 30 °C but they need generator temperatures higher than 140 °C to reach evaporator temperatures as low as −5 °C. The highest coefficients of performance can be achieved with triple-effect systems but they are the most complex, they require the highest generator temperatures and they should be mainly used for air conditioning.

Performance improvement of ammonia/absorbent air source absorption heat pump in cold regions

Air source absorption heat pump is promising in energy saving and emission reduction of heating and domestic hot water, but performs badly or even cannot work in cold climate. The ammonia/absorbent air source absorption heat pump with low-pressure boosting is proposed to solve the problem. The hybrid air source absorption heat pump + compressor system is modeled and the compression ratio is optimized to obtain maximum primary energy efficiency. The integrated system is simulated with air temperature ranging from −30℃ to 10℃ and hot water temperature from 30℃ to 60℃. Comparative simulations on three working fluids reveal that NH3–LiNO3 system has the lowest compression ratio and the highest primary energy efficiency value. By pressure boosting, the air source absorption heat pump can operate under air temperatures as low as −30℃. Primary energy efficiency of the hybrid system is about 15–50% higher than that of coal boiler, showing great potential for heat supply in cold regions. Practical application: Heating and domestic hot water consumes a large amount of energy every year. Air source absorption heat pump can be a potential alternative to the traditional boiler systems in the point view of primary energy efficiency. However, air source absorption heat pump performs badly or cannot work when the air temperature is low. This paper presents a hybrid air source absorption heat pump with pressure boosting to improve the performance of the air source absorption heat pump heating system, making it operate under lower outdoor air temperatures with higher primary energy efficiency. The novel heat supply system is expected to make contributions to building energy saving as well as pollution reduction.

Crystallization Analysis and Control of Ammonia-Based Air Source Absorption Heat Pump in Cold Regions

Energy consumption of heating and domestic hot water is very high and will keep increasing. Air source absorption heat pump (ASAHP) was proposed to overcome the problems of low energy efficiency and high air pollution existing in boiler systems, as well as the problem of bad performance under low ambient temperatures for electrical heat pumps. In order to investigate the crystallization possibility of ammonia-salt ASAHP, crystallization margin (evaluated by solution mass concentration) at generating temperature ranging from 100 to 150°C, evaporating temperature from −30 to 10°C, and condensing temperature from 30 to 65°C are analyzed. To prevent the NH3–NaSCN solution from crystallizing, ASAHP integrated with pressure booster located between the evaporator and absorber is simulated. Analysis and comparisons show that NH3–NaSCN is easy to crystallize at relatively high generating temperature, low evaporating temperature, and low condensing temperature. But crystallization margin of NH3–LiNO3 can always stay above 5% for most conditions, keeping away from crystallization. Pressure booster can effectively avoid the crystallization problem that will take place in the NH3–NaSCN ASAHP system.

Energy analysis of a diffusion absorption cooling system using lithium nitrate, sodium thiocyanate and water as absorbent substances and ammonia as the refrigerant

A diffusion absorption cooling system is analyzed to determine the appropriate fluid for the unit, based on the coefficient of performance (COP) and operating conditions, by comparing lithium nitrate (LiNO3), sodium thiocyanate (NaSCN) and water (H2O) as absorbent substances and by using ammonia (NH3) as the refrigerant. The presence of crystallization in the system is analyzed as a function of the generator and absorber temperatures. Additionally, the effects on the efficiency of the system from adding the inert gas helium (He) or hydrogen (H2) are studied. A mathematical model is developed and compared to experimental studies reported in the literature. At an evaporator temperature of −15 °C, a generator temperature of 120 °C and absorber and condenser temperatures of 40 °C, the results show that the best performance is achieved by the NH3–LiNO3–He mixture, with a COP of 0.48. This mixture performs 27–46% more efficient than the NH3–NaSCN mixture. The NH3–H2O mixture is 52–69% less efficient than the NH3–LiNO3 mixture. However, when the evaporator runs at 7.5 °C, the NH3–H2O–He mixture achieves a more efficient COP than does the NH3–LiNO3–He mixture, and the NH3–NaSCN–He and NH3–LiNO3–He mixtures achieve the same COP when the evaporator is at 10 °C. At temperatures below 7.5 °C, the NH3–NaSCN–He mixture achieves a higher COP than does the NH3–H2O–He mixture. The NH3–LiNO3 mixture shows crystallization at higher temperatures in the generator than does the NH3–NaSCN mixture. Moreover, at the same evaporator temperature, the NH3–LiNO3 mixture works at activation temperatures lower than does the NH3–NaSCN mixture.

Comparisons of different working pairs and cycles on the performance of absorption heat pump for heating and domestic hot water in cold regions

In order to explore the suitable working pair and cycle style for heating and domestic hot water in cold region, single-stage and double-stage air source absorption heat pump (ASAHP) and ground source absorption heat pump (GSAHP) are modeled in this paper. Based on these models, the performance of absorption heat pump (AHP) at different generating temperatures, evaporating temperatures and condensing temperatures is simulated respectively when using NH3–H2O, NH3–LiNO3 and NH3–NaSCN as working fluid. The results indicate that NH3–LiNO3 requires lower generating temperature, and at the same time can work at lower evaporating temperature and higher condensing temperature than other solutions for the same heat pump cycle. Besides, the double-stage AHP is advantageous over single-stage AHP in utilizing low temperature driving source, operating in very cold climate and producing higher temperature hot water. Finally, combining the simulated performance with required hot water temperature and climate conditions, the applicability of different AHP cycles (single-stage or double-stage), heat sources (air source or ground source) and working pairs (NH3–H2O, NH3–LiNO3 or NH3–NaSCN) is analyzed in different regions respectively.

Effect of the NH3–LiNO3 concentration and pressure in a fog-jet spray adiabatic absorber

Abstract This paper presents the effect that both the ammonia concentration in an ammonia–lithium nitrate solution and the absorber pressure have on the adiabatic absorption of ammonia vapour by droplets generated by a fog-jet injector. The injector ensemble is located at 205 mm from the bottom of the absorber. The solution has an ammonia mass fraction varying from 0.419 to 0.586 and the absorber pressure varies from 429 to 945 kPa. This is representative of the operating conditions for conventional absorption chiller cycles, but also for advanced cycles such as those with a booster compressor located in series between evaporator and absorber. This leads to a higher than common pressure in the absorber. Results show approach to equilibrium factors higher than 0.83, being the mean value of the experiments 0.9. The absorption ratio obtained was between 0.008 and 0.07. The increase in pressure and inlet subcooling increases the absorption rate, whilst the increase in the ammonia mass fraction increases the approach to equilibrium factor, decreasing the absorption rate.

A study of a bubble absorber using a plate heat exchanger with NH3–H2O, NH3–LiNO3 and NH3–NaSCN

There is a continuous research effort being carried out worldwide on the development of absorption cooling systems with the objective of increasing their performance, one important area is the search for more efficient heat exchangers and alternative working fluids that can improve the performance of NH 3 –H 2 O and H 2 O–LiBr that are commonly used in commercial absorption refrigeration machines. In this work the study of a plate heat exchangers used as bubble absorbers with NH 3 –LiNO 3 and NH 3 –NaSCN as alternative working fluids is carried out. A mathematical model was developed in order to analyze the absorption process in a bubble absorber with NH 3 –H 2 O, NH 3 –LiNO 3 and NH 3 –NaSCN as working fluids using a plate heat exchanger at refrigeration conditions and low generator temperatures. The results show that NH 3 –H 2 O and NH 3 –NaSCN working fluids obtained higher absorber thermal loads and absorbed vapor mass values than NH 3 –LiNO 3 , the lower values for the latter were caused mainly by the high solution viscosity that decreases the efficiency of the absorption process. On the other hand, NH 3 –LiNO 3 obtained the highest COP value from a single effect absorption refrigeration system simulation, however, NH 3 –NaSCN obtained a higher COP than NH 3 –H 2 O; therefore NH 3 –NaSCN seems to be a good working fluid to be tested in an absorption machine. ► A bubble absorber is simulated with NH 3 –H 2 O, NH 3 –LiNO 3 and NH 3 –NaSCN working fluids. ► The analysis is realized with a plate heat exchanger at different working conditions. ► The NH3–LiNO 3 obtains lower absorption performance than NH 3 –H 2 O and NH 3 –NaSCN. ► The NH 3 –LiNO 3 has problems in the absorption process, due to the high viscosity. ► The NH 3 –NaSCN obtains better performance in an absorption cycle than NH 3 –H 2 O.

Numerical simulation and experimental results of horizontal tube falling film generator working in a NH3–LiNO3 absorption refrigeration system

This paper describes the work made at the Centro de Investigacion en Energia in the development of an absorption refrigeration system for cooling and refrigeration applications with a capacity of 10 kW. The single effect unit utilizes ammonia-lithium nitrate as working pair and it is air cooled. The generator is a falling film type with horizontal tubes where the heating oil flows inside the tube bank and the ammonia-lithium nitrate solution flows as a falling film on the tube outside, where it is heated and ammonia vapor is generated. The generator consists of tree columns and four rows per column of horizontal tubes. The system was tested at controlled conditions with heating oil obtained from an electric resistance heating loop. A numerical model of the horizontal falling film generator was developed that divided the system into three different thermal elements: the flow inside the tube, the heat conduction in the tube wall and the falling film solution flow. The mathematical model was tested and validated with experimental data and a study of the influence of the heat transfer coefficient for ammonia-lithium nitrate solution in the numerical model was carried out. A comparison between experimental and numerical data for the heat flux in the system and the temperature profiles in the oil and solution flows shown a good degree of correlation.

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100�C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH3–LiNO3) are selected as the working fluids and the calculation results for the two-staged cycle and the three-staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low-grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.

Study on a solar-driven ejection absorption refrigeration cycle

This paper deals with a solar-driven ejection absorption refrigeration (EAR) cycle with reabsorption of the strong solution and pressure boost of the weak solution. The physical model is described and the corresponding thermodynamic calculation is performed with the working pair NH3–LiNO3. It is demonstrated that the EAR cycle has obvious advantages as compared with the conventional absorption refrigeration cycle: (1) the controllable high absorption pressure allows for substantially high coefficients of performance by the action of a liquid–gas ejector in which the low-pressure refrigerant vapour is injected and pressurized as a result of the ejection of high-pressure solution; (2) internal steady operation can be realized for refrigeration cycles driven by unsteady heat sources, especially for solar energy, by adjusting the power input consumed by solution pumps under the condition of economical and reasonable utilization of electric energy. © 1998 John Wiley & Sons, Ltd.

Optimization of generator temperatures in two-stage dual-fluid absorption cycles operated by biogas

Generator temperatures in ammonia absorption systems at subfreezing evaporator conditions have been optimized to use the minimum volume of biogas required to operate two-stage dual-fluid cycles. In this dual-fluid cycle, a LiBrH2O absorption system is used at the first stage with ammonia absorption systems at the second stage. Three different refrigerant-absorbent combinations (NH3H2O, NH3NaSCN, NH3LiNO3) were selected for this study. The absorber at the second stage is cooled by the low temperature water-refrigerant from the evaporator at the first stage. Lowering the absorber temperature reduces the heat input to the generator, which lowers the generating temperature and improves the performance of the absorption systems at the second stage. The optimum generator temperatures and performance coefficients of the systems at the first and second stages and the overall two-stage dual-fluid cycles are presented graphically. A comparative study between the three ammonia systems used in the two-stage dual-fluid cycle has been carried out.